The understanding of bone formation or remodeling is of great importance in the treatment of all diseases involving the skeleton, especially osteoporosis. Investigations previously have shed light on the close interactions between one phase of remodeling, bone resorption, and the immune system. The major purpose of this proposal is to determine if T and/or B cells and/or mononuclear phagocytes influence bone resorption and bone remodeling. The investigators wish to determine if immunodeficient strains of mice (Nudes with no mature T cells; Motheaten with autoimmune properties of increased circulating lymphokines, increased macrophage responsiveness, decreased B cells, and abnormal suppressor T cell function) have abnormal bone remodeling by dynamic bone histomorphometric evaluation. If defects are found, an attempt will be made to correct the defect by immunological manipulation. They will also determine which subsets of T and/or B lymphocytes are required for OAF production in mice and will charecterize the interactions with macrophages in the production of OAF. The group will use mice depleted of T cells to see whether or not they have normal bone remodeling when stimulated with PTH or PGE2. Lastly, they will try to localize these cells of the immune system versus cells involved in bone remodeling activity by using specific antisera with histochemical techniques.